Acknowledging the severity of the technological glitches in Vermont’s new health insurance website, Gov. Peter Shumlin on Thursday issued a surprise announcement extending the deadline by which residents will have to enroll for policies in the new marketplace.

But key members of the administration have known since at least the middle of September of defects in Vermont Health Connect, some of which, they were told by outside consultants, were potentially substantial enough to derail the enrollment timeline.

In a 192-slide Power Point presentation, conducted Sept. 11 and 12 and prepared at the behest of the federal government, managers at the Department of Vermont Health Access detailed a range of “risks” in the online marketplace, and presented “workarounds,” “mitigation” plans, and “contingencies.”

The so-called “Operational Readiness Review” also includes a presentation from Gartner, Inc., a Connecticut-based tech consultant hired to review the website. Gartner concluded that Vermont Health Connect should be given “red” status — as opposed to ‘‘yellow’’ or ‘‘green’’ — “due to significant risks to meeting the October 1st deadline for Go-Live.”

In the document Gartner found that the most “critical risks” involved a lack of time for testing to remediate errors; the project schedule was compressed; and production environment delivery had been delayed.

The slide show — acquired through a public records request — also features concerns about things like insufficient training for navigators; the ability of consumers to enroll through the Web; and the lack of in-house manpower that might be needed to deal with the volume of paper applications in the event of online dysfunction.

That the administration knew about possible defects on the site isn’t revelatory — Shumlin, his health care czar Robin Lunge, and Commissioner of Vermont Health Access Mark Larson have long said there would be “hiccups” and “bumps in the road.” But as recently as last week Shumlin reassured the press that his team would have the problems solved in time to meet the Jan. 1 deadline by which Vermonters needed to have new plans, lest their existing policies lapse.

The new deadline gives residents until March 31 to make the transition, and will allow them to renew their existing policies for another three months. That move has prompted its own set of questions, including whether or not people who take advantage of the extension will be subject to a full yearly deductible for the three-month extension, or if it will be pro-rated based on the length of the term.

Asked by Vermont Public Radio’s Bob Kinzel on Vermont Edition on Friday whether he knew ahead of time how problematic the rollout might be, Shumlin said, “we did not know the magnitude of the challenges we were going to face.”